1. Field of the Invention
This invention relates generally to a storage rack system for articles loaded on pallets of the type adapted to be handled by lift trucks, and more particularly, to a storage rack system of the push-back type.
2. Description of the Prior Art
In about 1961 Frazier Industrial Company developed an order-picking system employing its "GLIDE-IN" racks, and described in its brochure entitled "The New Concept in Order-Picking Systems". This storage rack system eventually became known in the art as a push-back system. This system employs a cart, known as a "GLIDE-IN" cart, which has four bearing-type wheels adapted to ride on a track extending along the storage bay for a distance of two pallets deep, thereby providing double depth storage. The tracks are mounted on a slight incline to the horizontal so that the cart is always automatically in a forward position to receive a first load when the storage bay is empty. After the first pallet is placed on an empty cart by a fork truck, the cart remains in the forward position. When a fork truck with a second pallet load approaches the storage bay in the same elevation and is aligned with the first load, the fork truck with the second pallet load can be stored by gently nudging the first load rearwardly whereby the first load and the cart supporting the same is pushed back to the second depth position of the storage bay. The fork truck then leaves the second load on the track rails whereby the first load is automatically held in the back (two deep) position. This bay of the storage rack system is now fully loaded. To unload the storage bay with a fork truck, the reverse of the above-described procedure is performed. As soon as the forward pallet load is removed from the storage bay, the rear pallet load on the cart will roll forwardly to the forward position, known as the "pick" position.
The next system to be developed, in about 1982, was a cart system developed by the Highline Company. This cart system was a push-back system similar to the "GLIDE-IN" system described above. This system was sold under the tradename "HYPER-CART" and was adapted to store three pallets deep in a storage bay by the use of a lower cart and an upper cart. Each of the carts had three or four bearing type wheels on each side of the cart frame. Each cart road on a track comprised of a pair of right angle channels (known as structural angles) facing inwardly with separate tracks being provided for the lower cart and for the upper cart. The angles forming the track for the upper cart are positioned above the angles forming the track for the lower cart.
The next push-back system to be used in the art was a cart system sold by Speedrack, Inc. under its trademark "Speedcart". This system was adapted for storing three pallets deep and employed a lower cart and an upper cart provided with four flanged wheels, two wheels on each side of the cart frame. The track for the carts comprised a formed C-channel with the wheels of the upper cart riding on an outer portion of the horizontally extending web of the channel and the wheels of the lower cart riding on an inner portion of this horizontally extending web of the channel. U.S. Pat. Nos. 4,462,500 and 4,613,270 issued to Speedrack, Inc.
The next system to be developed in about 1984 was a cart system developed by INTERROLL Corporation and sold under its trademark "STACKRAIL". This was another type of push-back system for storing three pallets deep and utilized what was known in the art as a "flow track" which comprises a track formed by two inwardly facing C-channels supporting rollers spaced apart along the length of the track. Each storage bay was provided with a pair of spaced apart flow tracks each of which supported an inner carrier and an upper carrier comprised of a C-shaped formed channel with the flanges riding on the rollers and the pallets being supported by the web of the channels. This system provides a storage bay which was able to store three pallets deep and the track system was mounted at a slight incline to the horizontal so that the upper and lower pallet supports always tended to roll to the forward postiion of the storage bay.
The next system to be developed, in about 1985, was a system employing flow tracks similar to the INTERROLL system, the system being developed by the Interlake Company and sold under the tradename "PUSH BACK RAIL".
While the above-described three pallet deep systems were satisfactory, they were relatively expensive and there was a need for a less expensive storage rack system capable of handling three or more pallets deep in storage.